Devices which are typically referred to as Radio Frequency Identification (RFID) tags or RFID chips, are made possible by technologies like described in U.S. Pat. No. 3,713,148 and U.S. Pat. No. 4,384,288. These patents are hereby incorporated by reference. Numerous applications for RFID tags are known to those skilled in the art, e.g. product labeling and supply chain management in retail, applications in road toll systems, public transport systems, passports, long distance running, and tagging of animals and library books.
RFID tags can be divided in those with a passive RFID chip and those with an active RFID chip. The passive RFID chips are dependent for the electrical energy to function on the wireless signal from a reader or interrogator device. When the signal transmitted from such a device is picked up by the antenna of the RFID chip it is transformed into electrical energy which allows the RFID chip to function, comprising the following of commands when those are simultaneously enclosed in the signal coming from the reader/interrogator (e.g. storing transmitted information in a memory when that is present, or deleting information from that memory) and sending a signal back to the reader/interrogator.
The active RFID chips have a battery on board for their energy supply. Because of that, they can actively send a signal out that can be picked up by a reading device. This also means that tags with such RFID chips can be detected at much larger distances than tags with passive RFID chips, but because of the battery the former tags can not be made as small as the latter and they also cost more.
Relatively recently an RFID inventory system at item level was described in patent application US-A-2007/019070, which is also hereby incorporated by reference. Furthermore, various applications of RFID tags in health care were described in references 1-4 in the list on page 18, which publications are also hereby incorporated by reference. For tracking biological tissue cassettes in hospital pathology departments, RFID tags attached to tissue cassettes have been described in U.S. patent applications US-A-2006/239867 and US-A-2006/031012, which are also hereby incorporated by reference.
However, in modern day pathology more and more procedures regarding tissue sample processing are speeded up by steps that involve the use of a microwave oven (e.g. tissue fixation and tissue decalcification). Since RFID tags contain an integrated circuit connected to an antenna, the electronic parts will be destroyed by the electromagnetic field in a microwave oven.
Therefore, tissue cassettes to which an RFID tag is permanently attached, or tissue cassettes in which an RFID tag has been incorporated in an inseparable way, cannot be used in tissue processing that involves the use of a microwave oven. That limitation poses a problem for the implementation of the use of such tissue cassettes and RFID technology in pathology.
Furthermore, RFID tags which are attached to the outside of tissue cassettes run the risk of being damaged when excess paraffin is scraped off the cassette after the embedding in paraffin of a processed sample of biological tissue and the tissue cassette in which the sample was processed. RFID tags attached to the outside of the long side walls of tissue cassettes also run the risk of being damaged when the tissue cassette (after said embedding and scraping off the excess paraffin) is clamped in a microtome for cutting sections of the biological tissue sample. In this respect it should be noted that the angular side of a tissue cassette, which would not be touched by the claws of the clamp in a microtome, should not be covered by attaching an RFID tag, since most pathology labs would like to use that space for a registration number or other code to enable visual recognition in case of a failure of the electronic equipment that is used to read the information in the RFID chip. These risks form problems for labeling tissue cassettes on the outside with RFID tags. Furthermore, RFID tags that would block the holes in the bottom of the tissue cassette and/or the holes in the lid that is used to close the tissue sample chamber of the tissue cassette cannot be applied, since a flow of fluids through those holes during processing of a tissue sample enclosed in the tissue sample chamber and a flow of fluid paraffin during said embedding is necessary.
When applying RFID tags which are attached to tissue cassettes with an adhesive like a glue, it is required that the adhesive can resist all the chemicals which are used in the processing of tissue samples in tissue cassettes and that after the tissue samples and the cassettes have been embedded in paraffin, the adhesive will hold for at least 100 years. Such requirements form a problem for labeling tissue cassettes with RFID tags using an adhesive like a glue.
The present invention offers a solution for these problems.